JP2024081732A - Activation and deactivation of purge unit of vapor compression system based at least in part on conditions within condenser of the vapor compression system - Google Patents

Abstract

To provide a vapor compression system for reducing power consumption of a purge unit and the vapor compression system as a whole in order to prevent or alleviate the lowering of efficiency caused by the substantial accumulation of non-condensables in a condenser.SOLUTION: A vapor compression system comprises a refrigerant loop. The refrigerant loop comprises a condenser 34, an expansion device 36, an evaporator 38 and a compressor 32. The compressor comprises: a liquid refrigerant temperature sensor 86 arranged in a shell; a total pressure sensor 88; and a processor 44. The processor 44 is configured to: receive, from the liquid refrigerant temperature sensor 86, a first signal indicating a liquid refrigerant temperature in the condenser 34; receive, from the total pressure sensor 88, a second signal indicating a total pressure of refrigerant vapor and a non-condensable gas in the condenser 34; determine an observed saturation temperature of the condenser and a predicted saturation temperature based, at least partially, on the first signal and the second signal; and selectively activate a purge unit 80 when the observed saturation temperature exceeds the predicted saturation temperature by more than a threshold amount.SELECTED DRAWING: Figure 3

Description

This application relates generally to vapor compression systems used in air conditioning and refrigeration applications.

Vapor compression systems utilize a working fluid, commonly referred to as a refrigerant, that changes phase between a vapor, a liquid, and combinations thereof in response to exposure to various temperatures and pressures associated with the operation of the vapor compression system. For example, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system may include a chiller, which is a type of vapor compression system that circulates a refrigerant to remove heat (e.g., cool) from a stream of water through tubes that extend through the chiller's evaporator. The cooled stream of water may be directed to a nearby structure to absorb heat (e.g., cool), and then circulated back to the chiller's evaporator to be cooled again.

Certain chillers utilize low pressure refrigerants, which means that portions of the chiller may operate below atmospheric pressure. Therefore, if this portion of the chiller is defective, non-condensables (e.g., air, atmospheric gases) may enter the chiller and become trapped. The presence of non-condensables generally reduces the efficiency of the chiller, as the chiller consumes more power as it tries to maintain its cooling capacity.

Certain chillers include a purge unit that removes noncondensables from the chiller. For example, the purge unit may include a separate (secondary) vapor compression system that is used to cool and condense refrigerant from a mixture of refrigerant vapor and noncondensables extracted from the chiller. The purge unit then returns the condensed liquid refrigerant to the chiller and exhausts the noncondensables, which, with the noncondensables removed, return the chiller to its normal efficiency.
However, purge units also consume power when in operation and can reduce the efficiency of the chiller system.

1 is a perspective view of a building that may utilize an embodiment of a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system in a commercial environment, in accordance with an embodiment of the present technique; FIG. 1 is a perspective view of an embodiment of a vapor compression system, in accordance with an embodiment of the present technique; 3 is a schematic diagram of an embodiment of the vapor compression system of FIG. 2, in accordance with an embodiment of the present technique. 3 is a schematic diagram of another embodiment of the vapor compression system of FIG. 2, in accordance with an embodiment of the present technique. 3 is a perspective view of the condenser side of an embodiment of the vapor compression system of FIG. 2, in accordance with an embodiment of the present technique. 6 is a schematic cross-sectional view of a condenser of the vapor compression system of FIG. 5, in accordance with an embodiment of the present technique. 1 is a flow diagram illustrating an embodiment of a process for activating and deactivating a purge unit of a vapor compression system depending on particular conditions within a condenser, in accordance with an embodiment of the present technique. 1 is a diagrammatic view of an embodiment of a purge unit, in accordance with an embodiment of the present technique; 11 is a flow diagram illustrating an embodiment of a purge process for a purge unit, in accordance with an embodiment of the present technique. 11 is a flowchart illustrating one embodiment of a standard purge mode of operation of a purge unit, in accordance with one embodiment of the present technique. 11 is a flow diagram illustrating an embodiment of an extended purge mode of operation of a purge unit, in accordance with an embodiment of the present technique. 11 is a graph of refrigerant to air ratio versus pump out time in a purge unit in accordance with an embodiment of the present technique.

As discussed above, non-condensables leaking into a vapor compression system, such as a chiller, generally reduce the efficiency of the system. Certain vapor compression systems include a purge unit to remove these non-condensables, but the purge unit generally consumes power and therefore reduces the efficiency of the system when in operation. With this in mind, the present embodiments are directed to a purge unit of a vapor compression system and a method of control thereof that improves efficiency by selectively activating and deactivating the purge unit in response to one or more conditions, such that the refrigerant-to-air ratio in the purge unit may be within certain industry standards, while minimizing the purge cycle duration, for example. As discussed below, these conditions include conditions in the chiller's condenser, time since the last purge operation, time since the last discharge of non-condensables, and combinations thereof. By reducing the time that the purge unit is in operation without removing a significant amount of non-condensables from the vapor compression system, the present embodiments reduce power consumption for the purge unit, and the vapor compression system as a whole, while still providing for preventing or mitigating the loss of efficiency due to significant accumulation of non-condensables in the vapor compression system's condenser.

Turning now to the drawings, FIG. 1 is a perspective view of one embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system 10 for a building 12 in a typical commercial environment. The HVAC&R system 10 may include a vapor compression system 14 that provides chilled liquid that may be used to cool the building 12. The HVAC&R system 10 may also include a boiler 16 that provides warm liquid to heat the building 12, and an air distribution system that circulates air through the building 12. The air distribution system may also include an air return duct 18, an air supply duct 20, and/or an air handler 22. In some embodiments, the air handler 22 may include a heat exchanger connected to the boiler 16 and the vapor compression system 14 by a conduit 24. The heat exchanger of the air handler 22 may receive either heated liquid from the boiler 16 or chilled liquid from the vapor compression system 14, depending on the operating mode of the HVAC&R system 10. Although the HVAC&R system 10 is shown with individual air conditioners on each floor of the building 12, in other embodiments, the HVAC&R system 10 may include air conditioners 22 and/or other components that may be shared between floors.

2 and 3 are an embodiment of a vapor compression system 14 that may be used in the HVAC&R system 10. The vapor compression system 14 may circulate a refrigerant in a circuit that begins with a compressor 32. The circuit may also include a condenser 34, an expansion valve or device 36, and a liquid chiller or evaporator 38. The vapor compression system 14 may further include a control board 40 having an analog-to-digital (A/D) converter 42, a microprocessor 44, non-volatile memory 46, and/or an interface board 48.

Some examples of fluids that may be used as refrigerants in vapor compression system 14 include hydrofluorocarbon (HFC) based refrigerants such as R-410A, R-407, R-134a, hydrofluoroolefins (HFOs), ammonia (NH ₃ ), R-717, carbon dioxide (CO ₂ ), R-744, or hydrocarbon based refrigerants, “natural” refrigerants such as water vapor, or any other suitable refrigerant. In some embodiments, vapor compression system 14 may be configured to efficiently utilize refrigerants having a normal boiling point of about 19 degrees Celsius (66 degrees Fahrenheit) at a pressure of 1 atmosphere, also referred to as low pressure refrigerants as opposed to medium pressure refrigerants such as R-134a. As used herein, “normal boiling point” may refer to the boiling point temperature measured at a pressure of 1 atmosphere.

In some embodiments, the vapor compression system 14 may use one or more of a variable speed drive (VSD) 52, an electric motor 50, a compressor 32, a condenser 34, an expansion valve or device 36, and/or an evaporator 38. The electric motor 50 may drive the compressor 32 and may be driven by the variable speed drive (VSD) 52. The VSD 52 receives alternating current (AC) power from an AC power source having a particular fixed line voltage and fixed line frequency and provides power to the electric motor 50 having a variable voltage and frequency. In other embodiments, the electric motor 50 may be powered directly from an AC or direct current (DC) power source. The electric motor 50 may include any type of electric motor that may be driven by a VSD or that may be powered directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable electric motor.

The compressor 32 compresses the refrigerant vapor and delivers the vapor to the condenser 34 via a discharge passage. In some embodiments, the compressor 32 can be a centrifugal compressor. The refrigerant vapor delivered by the compressor 32 to the condenser 34 can transfer heat to a cooling fluid (e.g., water or air) in the condenser 34. The refrigerant vapor can condense to a refrigerant liquid in the condenser 34 as a result of the heat transfer with the cooling fluid. The liquid refrigerant from the condenser 34 can flow through the expansion device 36 to the evaporator 38. In the embodiment shown in FIG. 3, the condenser 34 is water-cooled and includes a tube bundle 54 connected to a cooling tower 56, which supplies the cooling fluid to the condenser.

The liquid refrigerant delivered to the evaporator 38 may also absorb heat from another cooling fluid, which may or may not be the same as the cooling fluid used in the condenser 34. The liquid refrigerant in the evaporator 38 may also undergo a phase change from liquid refrigerant to a refrigerant vapor. As shown in the embodiment shown in FIG. 3, the evaporator 38 may include a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. The evaporator 38 cooling fluid (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator 38 via the return line 60R and exits the evaporator 38 via the supply line 60S. The evaporator 38 may reduce the temperature of the cooling fluid in the tube bundle 58 by heat transfer with the refrigerant. The tube bundle 58 of the evaporator 38 may include multiple tubes and/or multiple tube bundles. In any case, the vapor refrigerant exits the evaporator 38 and returns to the compressor 32 by a suction line to complete the cycle.

FIG. 4 is a schematic diagram of a vapor compression system 14 with an intermediate circuit 64 incorporated between the condenser 34 and the expansion device 36. The intermediate circuit 64 may have an inlet line 68 that is directly fluidly connected to the condenser 34. In other embodiments, the inlet line 68 may be indirectly fluidly connected to the condenser 34. As shown in the embodiment illustrated in FIG. 4, the inlet line 68 includes a first expansion device 66 disposed upstream of an intermediate vessel 70. In some embodiments, the intermediate vessel 70 may be a flash tank (e.g., a flash intercooler). In other embodiments, the intermediate vessel 70 may be configured as a heat exchanger or a "surface economizer." In the embodiment illustrated in FIG. 4, the intermediate vessel 70 is used as a flash tank, and the first expansion device 66 is configured to reduce the pressure (e.g., expand) of the liquid refrigerant received from the condenser 34. During the expansion process, a portion of the liquid may evaporate, and thus the intermediate vessel 70 may be used to separate the vapor from the liquid received from the first expansion device 66. Additionally, the intermediate vessel 70 may provide further expansion of the liquid refrigerant due to the pressure drop the liquid refrigerant experiences as it enters the intermediate vessel 70 (e.g., the pressure drop due to the sudden increase in volume it experiences as it enters the intermediate vessel 70). The vapor in the intermediate vessel 70 may be drawn by the compressor 32 through a suction line 74 of the compressor 32. In other embodiments, the vapor in the intermediate vessel may be drawn into an intermediate stage (e.g., other than the suction stage) of the compressor 32. The liquid that collects in the intermediate vessel 70 may be at a lower enthalpy than the liquid refrigerant exiting the condenser 34 due to the expansion in the expansion device 66 and/or the intermediate vessel 70. The liquid from the intermediate vessel 70 may then flow through line 72 to the second expansion device 36 and to the evaporator 38.

It has now been found that during operation of the vapor compression system 14, non-condensables (e.g., air, atmospheric gases) that leak into the system tend to accumulate in the condenser 34. Accordingly, as shown in FIGS. 3 and 4, the vapor compression system 14 includes a purge unit 80 fluidly connected to the condenser 34. As shown, the purge unit 80 receives a purge vapor stream 82 (e.g., a mixture of refrigerant vapor and non-condensables) from the condenser 34. After condensing the refrigerant vapor of the received purge vapor stream 82 to liquid refrigerant and removing the non-condensables, the purge unit 80 returns a purge return stream 84 (e.g., condensed liquid refrigerant) to the condenser 34.

In certain embodiments, the control board 40 is communicatively connected to the purge unit 80 such that the microprocessor 44 of the control board 40 provides control signals to control the operation of the purge unit 80, as described in more detail below. For example, in certain embodiments, the control board 40 may be communicatively connected to several sensors of the vapor compression system 14 (e.g., liquid refrigerant temperature sensor 86, total pressure sensor 88, other sensors in the purge unit 80). The control board 40 may provide appropriate control signals to activate or deactivate the purge unit 80 in response to data signals received from these sensors, in response to elapsed time (e.g., time since the purge unit 80 was last activated, time since noncondensables were last discharged by the purge unit 80), or in response to a combination thereof.

5 is a perspective view of an embodiment of a vapor compression system 14 according to the present technique. More specifically, FIG. 5 shows a condenser side 90 of the vapor compression system 14. Additionally, FIG. 6 is a schematic cross-sectional view of an embodiment of the condenser 34 shown in FIG. 5. As shown in these figures, the condenser 34 generally includes a discharge baffle 92 and a tube bundle 94 having a number of tubes 96 disposed within a shell 98. Additionally, the condenser 34 includes a vapor inlet 100 disposed at or near a top 102 of the condenser 34 and a liquid refrigerant outlet 104 disposed at or near a bottom 106 of the condenser. The illustrated condenser 34 also includes a purge extraction outlet 108 and a purge return inlet 110 that extend through the shell 98 and allow gas and liquid flow (e.g., purge vapor flow 82, purge return flow 84) between the interior of the condenser 34 and the purge unit 80.

More specifically, during operation of the vapor compression system 14, the illustrated condenser 34 generally receives a vapor flow 112 (e.g., a flow of refrigerant vapor, possibly contaminated with one or more non-condensable gases) through a vapor inlet 100 disposed near the top 102 of the condenser 34. More specifically, as shown in FIGS. 5 and 6, the vapor flow 112 is received from the compressor 32 at or near the center 114 of the length 116 (e.g., axial length) of the condenser 34. As shown, the flow of refrigerant vapor 112 impinges on a discharge baffle 92 disposed at the top 118 of the condenser 34 (e.g., above the condenser liquid level 120). The discharge baffle 92 generally directs the flow axially, as indicated by arrow 122, toward the end 126 of the condenser. The vapor flow 112 passes through openings 124 in the discharge baffle 92 (e.g., located near the end 126 of the condenser 34), as indicated by arrow 125, and is subsequently condensed on the surfaces of the condenser tubes 96 of the tube bundle 94. The condensed liquid refrigerant collects at a particular liquid level (e.g., the condenser liquid level 120) and then exits the condenser 34 through a liquid refrigerant outlet 104 located near the bottom 106 of the condenser 34, and continues to circulate through the vapor compression system 14 (e.g., to the expansion device 36 shown in FIG. 3).

As shown in FIG. 6, the tube bundle 94 may define one or more arrangements of layers or rows of tubes 96, such as row 128. In some embodiments, the tubes 96 of the tube bundle 94 may not include a discernible row (e.g., the tubes 96 of the tube bundle 94 may be arranged in a relatively random arrangement). The tubes 96 may be arranged in a fixed spacing arrangement such that each tube 96 is equally spaced from one another. However, in other embodiments, the tubes 96 may be arranged in a variable spacing arrangement such that the distances between the tubes vary from one another. In still further embodiments, the tubes 96 may be arranged in at least a partially fixed spacing arrangement. As such, some tubes 96 may be equally spaced from one another and other tubes 96 may be spaced at different distances from one another. It will be appreciated that in other embodiments, any other suitable arrangement of the tubes 96 may be used in accordance with the present disclosure.

As mentioned above, it is now known that non-condensables are generally trapped somewhere within the upper portion 118 of the condenser 34 (e.g., above the condenser liquid level 120) during operation of the vapor compression system 14. Thus, in certain embodiments, the purge vapor flow 82 directed to the purge vapor inlet 130 of the purge unit 80 for removal of these non-condensables is extracted from the purge extraction outlet 108 of the condenser 34 located at any suitable location within the upper portion 118 of the condenser 34. Additionally, in the illustrated embodiment, the purge unit 80 includes a gravity feed drain (e.g., a purge return outlet 132) to return the flow of condensed liquid refrigerant 84 to the condenser 34 via a drain 133. Thus, the illustrated condenser 34 includes a purge return inlet 110 located a vertical distance 134 below the purge return outlet 132 of the purge unit 80 and above the condenser liquid level 120.

Furthermore, in certain embodiments, the purge return outlet 132, the purge return inlet 110, and/or the exhaust 133 may include at least one separation mechanism 135. For example, in certain embodiments, the separation mechanism 135 may be a solenoid valve, a check valve, a P-trap, or a combination thereof. In the illustrated embodiment, the separation mechanism 135 operates by selectively isolating the purge unit 80 from the chiller (e.g., from the condenser 34), particularly while the purge unit 80 is removing non-condensables separated from the refrigerant (e.g., while the vacuum pump 190 is operating, as described below with respect to FIG. 8). In embodiments in which the separation mechanism 135 is an actively controlled solenoid valve or other actively controlled mechanism, the separation mechanism 135 is communicatively connected to a suitable control circuit (e.g., the control board 40) that provides signals that control the operation (e.g., open and close) of the separation mechanism 135 to selectively allow or block fluid flow between the purge return outlet 132 and the purge return inlet 110.

It will be appreciated that in other embodiments, the purge return outlet 132 may alternatively be fluidly connected to the evaporator 36 and may alternatively return the flow of condensed liquid refrigerant 84 to the evaporator without substantially affecting the performance of the vapor compression system 14. It will also be appreciated that in various embodiments, the purge unit 80 may be located on the same side of the condenser 34 as the evaporator 38 (e.g., between the condenser 34 and the evaporator 38), inside the condenser 34 (e.g., opposite the evaporator 38), or in any other suitable location in accordance with the present disclosure. Thus, for such embodiments, the purge extraction outlet 108 and/or the purge return inlet 110 may similarly be located on the same side of the condenser 34 as the evaporator 38 (e.g., between the condenser 34 and the evaporator 38).

The exemplary embodiment of the condenser 34 shown in FIG. 6 also includes a liquid refrigerant temperature sensor 136 and a total pressure sensor 138 (e.g., pressure transducer 138). As shown, the liquid refrigerant temperature sensor 136 is positioned below the condenser liquid level 120 to ensure proper measurement of the temperature of the liquid refrigerant in the condenser 34. As shown, the total pressure sensor 138 is positioned above the condenser liquid level 120 (e.g., in the top 118 of the condenser 34) to ensure proper measurement of the total pressure of the refrigerant and non-condensables at the top 118 of the condenser 34. In certain embodiments, the liquid refrigerant temperature sensor 136 and the total pressure sensor 138 provide data signals to the microprocessor 44 of the control board 40 or other suitable processing circuitry such that the microprocessor 44 of the control board 40 can activate and deactivate the purge unit 80 based at least in part on the measurements of the sensors 136 and 138.

As a particular example, FIG. 7 illustrates an exemplary embodiment of a process 150 that the microprocessor 44 of the control board 40 or other suitable processing circuitry of the vapor compression system 14 may execute (e.g., via executable instructions stored in memory) to determine when to selectively activate and deactivate the purge unit 80 in response to particular conditions in the condenser 34. It will be appreciated that other control strategies may additionally or alternatively be used in accordance with the present disclosure. The process 150 illustrated in FIG. 7 begins with the microprocessor 44 receiving a data signal from the liquid refrigerant temperature sensor 136 indicating the temperature of the liquid refrigerant in the condenser 34 (block 152). In a particular embodiment, the microprocessor 44 uses the temperature indicated by the liquid refrigerant temperature sensor 136 as a direct indication or representation of the observed condenser saturation temperature (OCST). The microprocessor 44 also receives a data signal from the total pressure sensor 138 of the condenser 34 (block 154). The microprocessor 44 then determines a predicted condenser saturation temperature (PCST) of the condenser 34 (block 158). For example, the microprocessor 44 may access a look-up table or use a formula stored in the non-volatile memory 46 of the control board 40 relating the measured total pressure to the PCST to determine or calculate the PCST for a particular refrigerant in the vapor compression system 14.

Continuing with the process 150 shown in FIG. 7, the microprocessor 44 then compares the OCST determined in the block above with the PCST (block 158). If the microprocessor 44 determines that the OCST (from block 152) exceeds the PCST (from block 156) by more than a certain threshold amount or deviation (e.g., 0.5°F, 0.75°F, 1°F), the microprocessor 44 activates the purge unit 80 if it is not already activated or when it is not activated (block 160). In certain embodiments, the microprocessor 44 or other suitable processing circuitry may activate the purge unit 80 for a specified length of time or purge period (e.g., 1 hour, 2 hours, 6 hours, 12 hours), until a certain condenser condition is met (e.g., until the PCST is again within the threshold of the OCST), until the purge unit 80 stops emitting non-condensables for a predetermined time, or combinations thereof. For the embodiment shown in FIG. 7, if the microprocessor 44 determines that the OCST does not exceed the PCST by more than a certain amount of threshold or deviation (block 158), the microprocessor 44 deactivates (stops) the purge unit 80 if or when the purge unit 80 is activated (block 162). In other embodiments, the microprocessor 44 or other suitable processing circuitry may provide appropriate control signals to activate or stop the purge unit 80 based on both the comparison of the OCST and the PCST described above and other factors (e.g., the time since the purge unit 80 was activated, the time since the purge unit 80 discharged noncondensables, etc.).

8 is a schematic diagram illustrating one embodiment of a purge unit 80 in accordance with the present technique. The illustrated purge unit 80 includes a vapor compression system 170 that is independent (e.g., secondary) to the primary vapor compression system 14 (e.g., chiller 14) being purged. As such, the illustrated embodiment of the purge unit 80 includes a compressor 172, a condenser 174 having a fan 176, a filter dryer 178, an expansion valve 180, and an evaporator coil 182 fluidly connected together to form a refrigeration loop or circuit 184 of the illustrated embodiment of the vapor compression system 170.

When the purge unit 80 shown in FIG. 8 is in operation, the refrigerant (e.g., R404a or another suitable refrigerant) is liquefied by the combined action of the compressor 172 and the condenser 174 and then introduced into the evaporator coil 182 disposed within the purge tank 186 to condense the purge vapor stream 82 flowing into the purge tank 186. More specifically, in the illustrated embodiment, the purge tank 186 receives the purge vapor stream 82 (e.g., a supply of refrigerant vapor and non-condensables) from the purge extraction outlet 108 of the condenser 34 of the primary vapor compression system 14 (e.g., the chiller 14). The refrigerant vapor of the purge vapor stream 82 that condenses within the purge tank 186 is returned to the purge return inlet 110 of the condenser 34 as a purge return stream 84 (e.g., a liquid refrigerant stream). As described in more detail below, non-condensable gases 188 in the purge vapor stream 82 received from the primary vapor compression system 14 that do not condense in the purge tank 186 are then removed by a vacuum pump 190.

The purge unit 80 shown in FIG. 8 includes a controller 192 communicatively connected to various components of the purge unit 80 to control the operation (e.g., on, off, drain) of the purge unit 80. In the illustrated embodiment, the controller 192 includes a memory 194 for storing instructions and a processor 196 for executing these instructions to control the operation of the purge unit 80. In other embodiments, the controller 192 may be the control board 40, and the microprocessor 44 may execute instructions stored in the non-volatile memory 46 to control the operation of the purge unit 80 in addition to the primary vapor compression system 14 and/or the HVAC&R system 10 as described above. In certain embodiments, the controller 92 may be distinct from the control board 40 and communicatively connected to the control board 40 to exchange data and/or control signals. For example, in such an embodiment, the processor 196 of the controller 192 may send data signals to the microprocessor 44 of the control board 40 to indicate whether the purge unit 80 is activated and whether there are any error messages or notifications being generated by the activated purge unit 80, as described in more detail below. Similarly, in such an embodiment, the microprocessor 44 of the control board 40 may send data signals to the processor 196 of the controller 192 to indicate measured or calculated parameters of the primary vapor compression system 14 (e.g., measured condenser liquid temperature, measured condenser pressure, calculated condenser saturation temperature) so that the controller 192 can determine when to selectively activate and deactivate the purge unit 80, as described in more detail below.

For the embodiment shown in FIG. 8, the controller 192 is communicatively connected to the various components of the purge unit 80 to receive data signals and/or provide control signals. For example, the processor 196 of the controller 192 may provide appropriate control signals to operate the compressor 172 and the fan 176 of the condenser 174 to operate the purge unit 80. The processor 196 of the controller 192 may provide appropriate control signals to operate a first solenoid valve 198, which remains in an open position except during the evacuation of non-condensables by the vacuum pump 190, as described below. Similarly, the processor 196 of the controller 192 may provide appropriate control signals to operate a second solenoid valve 200, which remains in a closed position except during the evacuation of non-condensables by the vacuum pump 190, as described below. The controller 192 may also provide appropriate control signals to operate and stop the vacuum pump 190 (e.g., to operate the vacuum pump 190 for a predetermined amount of pump-down time before stopping the pump). Additionally, the illustrated controller 192 may receive a data signal from a level sensor 199 indicative of the level of condensed liquid refrigerant in the purge tank 186.

Additionally, for the embodiment of the purge unit 80 shown in FIG. 8, the processor 196 of the controller 192 is communicatively connected to at least two temperature sensors. A first temperature sensor 202 measures the temperature (T1) of the purge unit refrigerant exiting the evaporator coil 182 of the purge unit 80, while a second temperature sensor 204 measures the temperature (T2) of the purge unit refrigerant entering the evaporator coil 182. It is currently understood that when the evaporator coil 182 is condensing refrigerant vapor from the primary vapor compression system 14, T1 generally increases (e.g., in absolute terms or relative to T2). However, when the purge tank 186 contains a significant amount of non-condensable gas, T1 decreases (e.g., approaches T2). Thus, as described below, the processor 196 of the controller 192, or other suitable processing circuitry, determines when to drain the purge tank 186 based at least on T1. For example, in certain embodiments, the processor 196 of the controller 192 can compare T1 to a predetermined threshold (e.g., 15 degrees Fahrenheit (°F)) and initiate draining of the purge tank 186 if T1 falls below (e.g., is less than) the predetermined threshold. In other embodiments, the processor 196 of the controller 192 can compare the difference between T1 and T2 to a predetermined threshold (e.g., 0.5°F, 1°F, 5°F) and initiate draining of the purge tank 186 if the difference between T1 and T2 falls below (e.g., is less than) the predetermined threshold.

For example, FIG. 9 is a flow diagram illustrating an exemplary embodiment of a purge process 220 whereby the processor 196 of the controller 192 of the purge unit 80, or other suitable processing circuitry of the vapor compression system 14, operates the purge unit 80. It will be appreciated that in other embodiments, the process 220 may include additional steps, omit steps shown, include simultaneous execution of multiple steps, and/or include execution of steps in a different order than shown in FIG. 9. In the illustrated example, the process 220 is executed when the microprocessor 44 of the control board 40 or the processor 196 of the controller 192 requests or triggers operation of the purge unit 80 for either a specified time, referred to herein as a "purge period," or an unlimited time (e.g., until interrupted).

The illustrated purge process 220 begins with the processor 196 resetting a counter that tracks the number of drains of the purge tank 186 during the current purge process (block 222) and recording the start time of the purge process. The processor 196 provides appropriate control signals to the compressor 172 and condenser fan 176 of the purge unit 80 (block 224) to operate both devices and to operate the purge unit 80. The processor 196 further provides appropriate control signals to open the first solenoid valve 198 (e.g., if it is determined to be in a closed state) and to close the second solenoid valve 200 (e.g., if it is determined to be in an open state) (block 226).

The embodiment of process 220 shown in FIG. 9 continues with the processor 196 receiving (block 228) a signal from the first temperature sensor 202 indicative of the temperature (T1) of the purge unit refrigerant exiting the evaporator coil 182 of the purge unit 80. The processor 196 analyzes T1 to determine whether to proceed with draining the purge tank 186. For the exemplary embodiment, the processor 196 determines (block 230) whether T1 is less than a predetermined temperature threshold (e.g., 15°F). In other embodiments, the processor 196 may compare the difference between T1 and T2 to various predetermined thresholds (e.g., 5°F, 10°F, 15°F).

Once the processor 196 determines that T1 has fallen below the predetermined temperature threshold, the processor 196 provides appropriate control signals to instigate or initiate draining of the purge tank 186, as indicated by the steps within brackets 232. For example, as shown, the processor 196 provides a control signal to operate the vacuum pump 190 for a predetermined amount of pump-down time (e.g., 30 seconds, 45 seconds, 1 minute) (block 234), close the first solenoid valve 198, and open the second solenoid valve 200 (block 236). The processor 196 further increments the purge count (block 238) and resumes the process 220 at block 222.

In the illustrated example, once T1 exceeds the predetermined temperature threshold in block 230, the processor 196 determines whether the purge period has expired or whether a purge interruption has been requested (block 240). For example, as illustrated, the processor 196 may compare the current time to the purge start time recorded in block 222 to determine whether the purge period has expired. The processor 196 may further check to see if it has been determined that the purge unit should be interrupted due to a change in conditions in the condenser (e.g., according to blocks 158 and 160 of FIG. 7). If the purge period has not expired and the purge process has not been interrupted, the processor 196 continues to receive a signal indicative of T1 (block 228) and continues to determine whether T1 has exceeded the predetermined temperature threshold (block 230) until the purge period has expired or the purge process has been interrupted (block 240). The processor 196 then provides appropriate control signals to shut down the compressor 172 and condenser fan 176 of the purge unit 80 (block 242), thereby shutting down the purge unit 80. In addition, as shown, the processor 196 may record in the memory 194 the purge end time and the purge count for this execution of the purge process 220.

In certain embodiments, the processor 196 or other suitable processing circuitry of the controller 192 of the purge unit 80 may operate the purge unit 80 in a standard purge mode of operation. An exemplary embodiment of a standard purge mode process 260 is shown in FIG. 10. In other embodiments, the specified purge and wait periods may be longer or shorter depending on the nature of the primary vapor compression system 14. It will be appreciated that in other embodiments, the process 260 may include additional steps, omit steps shown, include multiple steps performed simultaneously, and/or include performing steps in a different order than shown in FIG. 10.

As shown, the process 260 begins by operating a purge process (e.g., the purge process 220 shown in FIG. 9) for a predetermined purge period (e.g., 2 hours) (block 262). As described above, when the purge process 220 is completed, the memory 194 of the controller 192 may store a purge count and a purge end time. Thus, continuing with the process 260 shown in FIG. 10, the processor 196 then reviews the purge count value to determine whether draining of the purge tank 186 occurred during the operation of the purge process of block 262 (block 264). If the purge count indicates that one or more drains have occurred, the processor 196 again operates the purge process 220 for a purge period (e.g., 2 hours) (block 262). If the purge count indicates that no draining has occurred (e.g., the step in bracket 232 of the purge process 220 has not been performed), the processor 196 may proceed to the next step of the process 260.

For the illustrated embodiment, once the purge unit 80 has been operated (block 262) for a purge period (e.g., 2 hours) without being vented (block 264), the processor 196 waits at block 266 until a particular set of conditions are met to proceed. For the illustrated exemplary embodiment, the processor 196 receives data from sensors (e.g., liquid refrigerant temperature sensor 136, total pressure sensor 138 shown in FIG. 6) located within and communicatively connected to the condenser 34 of the primary vapor compression system 14 to determine the OCST and PCST of the condenser 34, as described above, or from another communicatively connected processor that has access to this data. Using these values, the processor 196 determines whether the OCST is greater than the PCS.
It is determined whether T is exceeded by more than a threshold or deviation value (DEV) (e.g., more than 0.5° F.) (block 266). If this condition is met or if the purge unit 80 has been shut off for at least a predetermined wait time (e.g., 6 hours based on the purge stop time) (block 266), the processor 196 proceeds to the next step in the process 260.

In the illustrated embodiment, the process 260 continues by again activating the purge process for a purge period (e.g., 2 hours) (block 268). The processor 196 then reviews the purge count to determine whether draining occurred during the purge process initiated in block 268 (block 270). As illustrated, if the processor 196 determines that draining of the purge tank 186 occurred, the processor 196 returns to block 262 of the process 260. If the processor 196 determines that draining did not occur (e.g., the step in bracket 232 of the purge process 220 was not performed), the processor 196 may wait a waiting period (e.g., 6 hours) with the purge unit 80 turned off (block 272) before returning to block 262 of the process 260. Thus, the embodiment of the standard purge mode process 260 shown in FIG. 10 limits the time that the purge unit 80 is activated to reduce power consumption and improve the efficiency of the primary vapor compression system 14 and the HVAC&R system 10.

In certain embodiments, the processor 196 or other suitable processing circuitry of the controller 192 of the purge unit 80 may operate the purge unit 80 in an extended purge mode of operation. An exemplary embodiment of an extended purge mode process 280 is shown in FIG. 11. In other embodiments, the specified purge and wait periods may be longer or shorter depending on the nature of the primary vapor compression system 14 (e.g., chiller 14). It will be appreciated that in other embodiments, the process 280 may include additional steps, omit steps that are shown, include multiple steps performed simultaneously, and/or include performing steps in a different order than shown in FIG. 11.

As shown, process 280 begins by resetting a counter of the number of days since the last drain of purge tank 186 (block 282) and resetting a counter of the number of purge cycles (for that day) (block 284). Processor 196 then operates a purge process (e.g., purge process 220 shown in FIG. 9) for a predetermined purge period (e.g., one hour) (block 286). If the purge count indicates that at least one drain has occurred during the purge process of block 286, as shown in block 288, processor 196 again resets the counter of the number of days since the last drain (block 290) and returns to block 284.

Continuing with the illustrated embodiment, if the processor 196 determines (block 288) that no draining occurred during the purge process of block 286 (e.g., the step in bracket 232 of purge process 220 was not performed), the processor 196 increments the purge unit cycle count and waits (block 292) with the purge unit 80 turned off for a first predetermined wait period (e.g., 4 hours). After waiting, the processor 196 determines (block 293) whether the purge unit cycles are greater than or equal to a predetermined value (e.g., 3), and if not, the processor 196 returns to block 286 to again perform the purge process for the purge period (e.g., 1 hour). If the processor 196 determines (block 293) that draining of the purge tank 186 has not occurred, the processor 196 increments (block 294) the number of days since the last drain and waits with the purge unit 80 shut off for a second waiting period (e.g., 24 hours), the second waiting period being substantially longer than the first waiting period. For example, in one embodiment, if the processor 196 determines that draining has not occurred for three or more one-hour operations of the purge process, with the purge unit shut off for four hours between each purge process, the processor 196 increments (block 295) the number of days since the last drain and waits with the purge unit 80 shut off for a second waiting period (e.g., 24 hours), the second waiting period being substantially longer than the first waiting period.
6 increments the number of days since the last drain and waits 24 hours with purge unit 80 shut off.

Continuing with the illustrated embodiment, once the second waiting period has expired, the processor 196 may determine (block 296) whether the number of days since the last drain is equal to or greater than a predetermined number of days (e.g., one week). If not, the processor 196 returns to block 284. If the processor 196 again determines (block 293) that draining of the purge tank 186 has not occurred between repeated activations of the purge process, the processor 196 again increments the number of days since the last drain (block 294) and waits with the purge unit off for a second waiting period (e.g., 24 hours). For example, in one embodiment, if the processor 196 determines that draining has not occurred for three or more one-hour activations of the purge process with the purge unit off for four hours between each purge process, the processor 196 increments the number of days since the last drain and waits for 24 hours with the purge unit off.

Thus, for the illustrated embodiment, if the processor 196 determines (block 296) that draining of the purge tank 186 has not occurred for a predetermined duration (e.g., one week) of the daily purge routine (e.g., operating the one-hour purge process at least three times with four-hour intervals), the processor 196 waits (block 298) with the purge unit 80 deactivated for a third waiting period (e.g., seven days) before returning to block 284 of the process 280, the third waiting period being substantially longer than the first and second waiting periods. As shown, the processor 196 then performs a day of the above-described purge routine (e.g., operating the one-hour purge process at least three times with four-hour intervals). If draining of the purge tank 186 has not occurred because the number of days since the last drain remains greater than the predetermined number of days (e.g., seven days), the processor 196 again waits (block 298) with the purge unit 80 deactivated for a third duration (e.g., one week) before returning to block 284 of the process 280. Thus, the embodiment of the extended purge mode process 280 shown in FIG. 11 substantially limits the time that the purge unit 80 is activated (e.g., compared to the standard purge mode process 260 shown in FIG. 10). More specifically, the extended purge mode process 280 allows for substantially better efficiency of the vapor compression system 14 by selectively shutting down the purge unit 80 when the purge unit 80 is not actively removing non-condensables from the primary vapor compression system 14 (e.g., when draining of the purge tank 186 is not occurring). Thus, the process 280 shown in FIG. 11 allows for further reductions in power consumption and increased efficiency of the primary vapor compression system 14 and the HVAC&R system 10.

It will be appreciated that various errors or problematic conditions may occur during operation of the purge unit 80, and in response, the processor 196 of the controller 192 of the purge unit 80 may provide control signals to generate warning messages to be provided to occupants or technicians. For example, if the processor 196 determines that T2 exceeds a first threshold temperature (e.g., 5° F.) during execution of the purge process 220 of FIG. 9, the processor 196 of the purge unit 80 may send an appropriate signal to warn that adjustment of the expansion valve 180 of the purge unit 80 may be necessary, as shown in FIG. 8. If the processor 196 determines that T2 exceeds a second threshold temperature (e.g., 10° F.), the processor 196 of the purge unit 80 may send an appropriate signal to again warn that adjustment of the expansion valve of the purge unit 80 may be necessary or that the second temperature sensor 204 may be defective, and a control signal to shut down the purge unit 80. If the processor 196 determines that the level sensor 199 indicates that the level of condensed liquid refrigerant in the purge tank 186 exceeds a particular threshold, the processor 196 may provide an appropriate signal to shut off the purge unit 80 for one minute and provide a warning that the purge unit 80 has been temporarily shut off while refrigerant is drained into the condenser 34 of the primary vapor compression system 14. In certain embodiments, if the processor 196 determines that the number of drains (e.g., purge count) within a 24-hour period is greater than a threshold value (e.g., 10, 20, 30, 40), the processor 196 provides a warning indicating that the daily purge count limit has been exceeded and that there may be a leak in the primary vapor compression system 14. Additionally, in certain embodiments, if the processor 196 determines that the OCST remains above the PCST by at least the DEV value for 24 consecutive hours, the processor 196 may provide a warning indicating a possible vent in the primary vapor compression system 14 and that maintenance of the purge unit 80 should be performed.

It will also be appreciated that in certain embodiments, the processor 196 of the controller 192 may be programmed to switch between different operating modes. For example, in certain embodiments, the processor 196 may be capable of switching between the standard purge mode process 260 and the enhanced purge mode process 280 as described above (e.g., in response to input from a user or technician, in response to conditions within the vapor compression system 14). Additionally, in certain embodiments, the processor 196 may support other purge unit operating modes for use during installation, maintenance, and/or repair of the primary vapor compression system 14 or the HVAC&R system 10. For example, in certain embodiments, in a service mode, the processor 196 may accept input from a communicatively connected user input device to operate the purge process 220 (e.g., as shown in FIG. 9 ) for a specified purge period (e.g., 12 hours, 24 hours, 72 hours, etc.). In certain embodiments, in manual mode, the processor 196 may accept input from a communicatively coupled user input device to operate the purge process indefinitely until another input (e.g., an interrupt signal) is received to stop the purge process. It will be appreciated that when operating in service or manual mode, one or more of the error or problem conditions (e.g., daily purge count limit) may be suppressed.

As described above with respect to FIGS. 3 and 4, the purge unit 80 is fluidly connected to the condenser 34 to receive a purge vapor stream 82 (e.g., a mixture of refrigerant vapor and non-condensables) from the condenser 34 and return condensed liquid refrigerant in a purge return stream 84 to the condenser 34 free of non-condensables. In addition to the condenser 34 being at a location within the primary vapor compression system 14 where non-condensables accumulate, it has now been found that certain locations within the interior space of the condenser 34 are better for extracting (e.g., capturing, removing) the purge vapor stream 82 in terms of the efficiency of the purge unit and the purge process 220.

For example, referring again to FIGS. 5 and 6, it is now known that certain locations within the top 118 of the condenser 34 are particularly turbulent and therefore have a higher refrigerant content relative to non-condensables. As such, it is now known that locating the purge extraction outlet 108 at a particular location within the top 118 of the condenser 34 can increase the purge efficiency relative to other locations. For example, prior to this disclosure, the purge extraction outlet 108 has been located near the top 102 of the condenser 34 (e.g., near the end 126 of the condenser 34), such as the location shown by arrow 300 in FIG. 5. Other purge extraction outlet locations include immediately above the condenser liquid level 120 near the end of the condenser 34, as shown by arrow 302. However, it is now known that, although these locations may contain non-condensables and may be used to extract the purge vapor flow 82 from the condenser 34, these locations are also particularly turbulent areas within the condenser 34. Therefore, locating the purge extraction outlet 108 near these locations involves operating the purge unit 80 for a longer period of time compared to other locations to substantially remove noncondensables from the vapor compression system 14.

In contrast, as shown in Figures 5 and 6, the purge extraction outlet 108 of the present disclosure is generally located below the discharge baffle 92 and above the condenser liquid level 120. More specifically, in certain embodiments, the purge extraction outlet 108 is located below the discharge baffle 92 and near the middle or center 114 of the length 116 of the condenser 34. As best shown in Figure 6, in certain embodiments, this corresponds to locating the purge extraction outlet 108 away from the top 102 of the condenser 34 and above the condenser liquid level 120. More specifically, the illustrated purge extraction outlet 108 may be described as being near the middle or center 304 of the height 306 (e.g., vertical height) of the condenser 34 (e.g., near the condenser tubes 96 of the tube bundle 94). It has now been found that locating the purge extraction outlet 108 as disclosed herein substantially improves the efficiency of the purge unit 80 and the vapor compression system 14 and HVAC&R system 10. For example, locating the purge extraction outlet 108 as disclosed herein may allow for about a 1 hour purge operation to be as effective as about a 12 hour purge operation from a different purge extraction location, such as from the top 102 of the condenser 34.

In certain embodiments, during operation of the purge unit 80, the temperature and pressure in the purge tank 186 may be used to represent the ratio of refrigerant to air in the vapor portion of the purge tank 186. For example, as shown in FIG. 8, in certain embodiments, at least one temperature sensor 308 and at least one pressure sensor 310 may be disposed in the vapor portion 312 of the purge tank 186 (e.g., above the liquid level 314 of the purge tank 186), and measurements from the temperature sensor 308 and the pressure sensor 310 may be used by the controller 192 to determine the ratio of the mass of refrigerant in the vapor portion 312 of the purge tank 186 to the mass of air in the vapor portion 312 of the purge tank 186.

As gas is pumped out of the purge tank 186, the pumped-out flow may combine with continued condensation on the evaporator coil 182 of the purge tank 186. If the purge tank 186 has a liquid seal in the drain, liquid boils and condenses to replace the volume pumped out of the chiller 14. Conversely, if the purge tank 186 does not have a liquid seal in the drain, flow is generated from the condenser through the drain line to replace that volume. In either case, the ratio of refrigerant in the pumped-out gas increases throughout the purge cycle.

In certain embodiments, the duration of the purge cycle may be reduced to a period where modeling and testing indicate that the average pump-out refrigerant-to-air ratio meets the specific requirements of an existing industry standard, such as ASHRAE 147/AHRI 580. For example, the controller 192 may receive temperature and pressure measurements from the temperature sensor 308 and pressure sensor 310, which may be used in combination with a dynamic model of the purge operation in the purge unit 80 (e.g., the purge tank 186 in certain embodiments) to determine when the refrigerant-to-air ratio in the purge unit 80 (e.g., the purge tank 186 in certain embodiments) meets the specific requirements of an existing industry standard, such as ASHRAE 147/AHRI 580. For example, in certain embodiments, the controller 192 may determine a minimum duration of a purge cycle, including a minimum duration of pump-out time in the purge unit 80, that allows the refrigerant-to-air ratio in the purge unit 80 (e.g., in the purge tank 186 in certain embodiments) to meet at least one industry standard.

In such an embodiment, for example, pump-out time in vacuum pump 190 may be reduced from about 30 seconds to about 5 to about 10 seconds, about 4 to about 15 seconds, or about 3 to about 20 seconds. Additionally, the temperature in purge tank 186 may be reduced by modifying the suction temperature for pump-out initiation and the coil saturation temperature. By doing so, the refrigerant to air ratio in purge tank 186 may be significantly reduced, for example, to less than about 2.5, less than about 2.0, less than about 1.5, or even less (e.g., about 1.0), as shown in FIG. 12. As used herein, the term "approximately" is intended to refer to a property that is very close to the stated value, as one of ordinary skill in the art would understand. For example, a particular property that is "approximately" equal to a particular stated value may be within a +/- 5% tolerance of the stated value, within a +/- 4% tolerance of the stated value, within a +/- 3% tolerance of the stated value, within a +/- 2% tolerance of the stated value, within a +/- 1% tolerance of the stated value, or even within a smaller tolerance range. As one non-limiting example, the embodiments described herein can significantly reduce the refrigerant to air ratio in purge tank 186 to approximately 1.0 (e.g., 0.95 to 1.05 assuming a +/- 5% tolerance).

In certain embodiments, the suction pressure of the compressor 172 of the secondary vapor compression system 170 may be controlled by the constant pressure expansion valve 316 to a very low saturated refrigerant pressure in the secondary refrigerant. In certain embodiments, the purge refrigerant may be a low temperature refrigerant such as R404a or R134a, or other refrigerants that can be used at low temperatures, such as propane, R1270, R1234yf, R1234ze, R407A, R452A, etc.

Similarly, in such an embodiment, the compressor 172 may be designed for a relatively low temperature, which results in a lower partial pressure of the refrigerant in the purge tank 186 and a lower refrigerant-to-air ratio in the purge tank 186. In addition, the short duration of the pump-out cycle minimizes the flow of displaced refrigerant into the purge tank 186 and does not significantly affect the overall refrigerant-to-air ratio in the purge tank 186. The embodiments described herein allow for existing industry standards for refrigerant-to-air ratios without the added cost of specific equipment such as exhaust gas canisters.

While only certain features and embodiments have been shown and described, those skilled in the art may conceive of numerous modifications and changes (e.g., variations in size, dimensions, structure, shape and proportions of various elements, parameter values (e.g., temperature, pressure, etc.), mounting configurations, material usage, color, orientation, etc.) without substantially departing from the novel teachings and advantages of the claimed subject matter. The order or sequence of any process or method steps may be changed or reordered in accordance with alternative embodiments. It is therefore to be understood that the appended claims are intended to encompass all such modifications and changes as are within the true spirit of the present disclosure. Moreover, in order to provide a concise description of exemplary embodiments, not all features of the actual embodiment may be described (i.e., those that are not relevant to the best embodiment of the present disclosure currently contemplated or to realizing the present disclosure as set forth in the claims). It is to be understood that in the development of any such actual embodiment, as in any engineering or design project, numerous embodiment-specific decisions may be made. While such a development effort might be complex and time-consuming, it would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill in the art having the benefit of this disclosure without undue experimentation.

Claims (20)

1. A refrigerant loop comprising a fluidly connected condenser, an expansion device, an evaporator, and a compressor, the condenser comprising:
A shell,
a liquid refrigerant temperature sensor disposed within the shell;
a total pressure sensor disposed within the shell;
a processor communicatively connected to the liquid refrigerant temperature sensor and the total pressure sensor, the processor comprising:
receiving a first signal from the liquid refrigerant temperature sensor indicative of a liquid refrigerant temperature at the condenser;
receiving a second signal from the total pressure sensor indicative of a total pressure of refrigerant vapor and non-condensable gases in the condenser;
determining an observed saturation temperature and a predicted saturation temperature of the condenser based at least in part on the first signal and the second signal;
and a processor configured to selectively activate a purge unit when the observed saturation temperature exceeds the predicted saturation temperature by more than a threshold amount. The vapor compression system of claim 1, wherein the threshold amount is approximately 0.5 degrees Fahrenheit (°F). The vapor compression system of claim 1, wherein the condenser comprises a plurality of tubes disposed within the shell and configured to condense a flow of refrigerant vapor into liquid refrigerant that collects at a liquid level at a bottom of the shell, the liquid refrigerant temperature sensor being disposed below the liquid level at the shell of the condenser, and the total pressure sensor being disposed above the liquid level at an upper portion of the shell of the condenser. The vapor compression system of claim 1, wherein the total pressure sensor is disposed near the top of the shell of the condenser. The vapor compression system of claim 1, wherein the processor is configured to selectively shut down the purge unit when the processor determines that the observed saturation temperature does not exceed the predicted saturation temperature by more than a threshold amount. The vapor compression system of claim 5, wherein the processor is configured to provide a control signal to shut down the compressor and condenser fans of the purge unit to selectively shut down the purge unit. The vapor compression system of claim 1, wherein the processor is configured to activate an alarm indicating a problem with the purge unit if the observed saturation temperature exceeds the predicted saturation temperature by more than the threshold amount for more than a predetermined time. The vapor compression system of claim 1, wherein the processor is configured to determine the predicted saturation temperature of the condenser from a look-up table stored in a memory of the vapor compression system based at least in part on the total pressure of the refrigerant vapor and non-condensable gas in the condenser. 2. The vapor compression system of claim 1, wherein the processor is configured to determine the predicted saturation temperature of the condenser by calculating the predicted saturation temperature based at least in part on the total pressure of refrigerant vapor and non-condensable gases in the condenser. To selectively activate the purge unit, the processor
Activating the compressor and condenser fan of the purge unit;
receiving a temperature of the refrigerant exiting the evaporator coil of the purge unit;
in response to determining that the temperature of refrigerant exiting the evaporator coil of the purge unit is below a minimum temperature threshold;
closing a first solenoid valve of the purge unit, the first solenoid valve being disposed between the condenser and the purge unit;
Opening a second solenoid valve of the purge unit, the second solenoid valve being disposed between a purge tank of the purge unit and a vacuum pump of the purge unit;
10. The vapor compression system of claim 1 configured to operate the vacuum pump for a predetermined pump-down period. 1. A vapor compression system comprising a purge unit fluidly connected to a condenser of the vapor compression system, the vapor compression system comprising a memory storing instructions and a processor configured to execute the instructions to control the purge unit, the instructions comprising:
receiving a first signal indicative of a liquid refrigerant temperature in a condenser from a liquid refrigerant temperature sensor located below a liquid level in the condenser of the vapor compression system;
receiving a second signal from the total pressure sensor located at an upper portion of the condenser indicative of a total pressure of refrigerant vapor and non-condensable gases in the condenser;
instructions for determining an observed saturation temperature and a predicted saturation temperature of the condenser based on the first signal and the second signal;
instructions for selectively activating the purge unit when the observed saturation temperature exceeds the predicted saturation temperature by more than a threshold amount;
A vapor compression system. The vapor compression system of claim 11, wherein the instructions include instructions to activate an alarm indicating a problem with the purge unit if the observed saturation temperature exceeds the predicted saturation temperature by more than the threshold amount for more than a predetermined time. The vapor compression system of claim 11, wherein the threshold amount is approximately 0.5°F. The vapor compression system of claim 11, wherein the instructions include instructions to selectively shut down the purge unit if the observed saturation temperature does not exceed the predicted saturation temperature by more than a threshold amount. The vapor compression system of claim 11, wherein the instructions include instructions to determine the predicted saturation temperature of the condenser from a look-up table stored in the memory based at least in part on the total pressure of refrigerant vapor and non-condensable gas in the condenser. The vapor compression system of claim 11, wherein the instructions include instructions for determining the predicted saturation temperature of the condenser by calculating the predicted saturation temperature based at least in part on the total pressure of refrigerant vapor and noncondensable gases in the condenser. The instructions for selectively activating the purge unit include:
commands to operate the compressor and condenser fan of the purge unit;
instructions to receive a temperature of a refrigerant leaving an evaporator coil of the purge unit;
in response to determining that the temperature of refrigerant exiting the evaporator coil of the purge unit is below a minimum temperature threshold;
closing a first solenoid valve of the purge unit, the first solenoid valve being disposed between the condenser and the purge unit;
Opening a second solenoid valve of the purge unit, the second solenoid valve being disposed between a purge tank of the purge unit and a vacuum pump of the purge unit;
and instructions to operate the vacuum pump for a predetermined pump-down time. The vapor compression system of claim 17, wherein the instructions include instructions to close a third solenoid valve associated with a discharge line of the purge unit prior to operating the vacuum pump in response to determining that the temperature of the refrigerant exiting the evaporator coil of the purge unit is below the minimum temperature threshold. 1. A method of operating a purge unit fluidly connected to a condenser of a vapor compression system, comprising:
receiving, via a processor of the vapor compression system, a first signal indicative of a liquid refrigerant temperature in a condenser from a liquid refrigerant temperature sensor located below a liquid level in the condenser of the vapor compression system;
receiving, via the processor, a second signal from a total pressure sensor disposed in an upper portion of the condenser indicative of a total pressure of refrigerant vapor and non-condensable gases in the condenser;
determining, via the processor, an observed saturation temperature of the condenser based on the first signal and a predicted saturation temperature of the condenser based on the second signal;
and selectively activating the purge unit in response to the processor determining, via the processor, that the observed saturation temperature exceeds the predicted saturation temperature by more than a threshold amount. 20. The method of claim 19, comprising selectively shutting down the purge unit in response to the processor determining that the observed saturation temperature no longer exceeds the predicted saturation temperature by more than the threshold amount.

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